Attention has been recently paid on the increasing number of railway, airport or harbor accidents caused by the collision of two or more vehicles driving on opposite directions, on a roadway in which traffic is normally allowed in one direction.
These accidents always have very serious consequences and may be often related to a poor or insufficient warning of the danger, which affects perception of the prohibition or danger sign by a possibly tired or careless driver.
Furthermore, a number of studies and researches in some European countries have shown that drivers increasingly tend to mistakingly or carelessly enter one-way roads in the wrong direction, such as at the exit of a highway or an expressway.
While case studies have not shown high occurrences, a great number of victims have been noted, thence the problem is relevant.
Although current signs are effective in good weather conditions, they have the drawback of not being equally perceivable in poor visibility conditions.
Road signs, even of the light-emitting type, are not effective in poor visibility conditions and further involve a considerable power consumption.
Also, in case of fog or rain, the effectiveness of such signs is further affected by the halo generated therearound.
Road markings tend to be even less perceivable in rain and fog conditions, and to be completely hidden under the snow.
Furthermore, such markings are exposed to deterioration, due to the passage of vehicles thereon, and cannot be readily made for temporary signalization.
DE-A1-4000630 discloses a wrong-way warning system which, by using sensors under the asphalt or photocells, triggers various devices to stop the wrong-way vehicle, while simultaneously signaling the danger situation to the drivers in the right direction.
Such system has the drawback of only providing a remedy to an error, without proposing any prevention thereof. Any vehicle driving in the right direction immediately upstream from the signaling station would unavoidably collide against the vehicle driving the wrong way. This drawback is even more serious when large and heavy vehicles are involved, such as ships, trains or aircrafts, which have a very long braking distance.
Patent GB-A-2226134 discloses and claims a laser beam security barrier.
Such prior art system has the drawback of only showing the obstacle, and is not suitable for present purpose: all prior art signs do not benefit from the laser beam and remain invisible, especially in low visibility conditions.
Another laser beam barrier, which also involves the above drawbacks, is disclosed in U.S. Pat. No. 6,259,365.
Obstacle detection systems, whether or not based on the use of a laser beam, are also known from EP-A2-1148460, U.S. Pat. Nos. 5,440,116, 6,278,360B1, DE-A1-3640539, DE-A1-10146974, U.S. Pat. Nos. 5,293,162, 5,914,661.
These prior art solutions all have the drawback of only detecting the obstacle at a given distance, when it might be too late, especially in bad weather conditions.